I was watching the Nova show, "Lost at Sea; The Search for Longitude", which describes our quest to accuately determine our longitude as we travel across the sea. It said that watching the moons of Jupiter was an accurate way of keeping the time of your home port but wasn't practical to do on the rolling ocean. This is fascinating! Can anyone either explain to me how to use Jupiter's moons as a timepiece or direct me to another resource? I'd think the fluctuations in each moon's orbit would create inconsistencies. It seems like jupiters relative position to Earth would create inconsistencies, too. Any insights?